This invention relates generally to a semiconductor exposure apparatus for transferring, by exposure, a fine pattern of a semiconductor integrated circuit, formed on a mask, onto a substrate such as a wafer. More particularly, the invention is concerned with a semiconductor exposure apparatus of proximity type wherein exposure is performed while a mask and a wafer (substrate) are placed in close proximity to each other with a small spacing maintained therebetween. In another aspect, the invention is concerned with a device manufacturing method using such exposure apparatus.
In proximity type exposure apparatuses, exposure is performed while a mask and a substrate such as a wafer are placed in close proximity to each other with a small spacing maintained therebetween. An X-ray exposure apparatus is a representative example of them, and Japanese Laid-Open Patent Application, Laid-Open No. 100311/1990 shows an X-ray exposure apparatus using a synchrotron radiation (SR) light source, as an example.
FIG. 5 is a schematic view of a general structure of an X-ray exposure apparatus. In FIG. 5, a mask 101 has a membrane 102 having a pattern formed thereon. The mask 101 is held by a mask chuck 103 which is mounted on a mask stage base 104, and it is positioned with respect to an X-ray light path. A wafer 106 (substrate) to be positioned opposed to and in close proximity to the mask 101, is held by a wafer chuck 107 which is mounted on a fine-motion stage 108 to be used for mask-to-wafer alignment. The wafer chuck 107 and the fine-motion stage 108 are mounted on a rough-motion stage 109 which is operable to move the wafer 106 stepwise so that exposure view angles on the wafer are sequentially placed in an X-ray irradiation region. A guide for the rough-motion stage 109 is fixed to a stage base 110.
Generally, in X-ray exposure apparatuses such as described above, the exposure operation is performed in accordance with a step-and-repeat method wherein the pattern on the membrane 102 is repeatedly printed on the wafer 106, and the mask membrane 102 and the wafer 106 are disposed opposed to each other with a small spacing of about 10-30 microns maintained therebetween (proximity exposure).
When, in such X-ray exposure apparatuses, the exposure is to be performed in accordance with a global alignment process, the procedure will be as follows:
(1) The rough-motion stage 109 moves the wafer 106 so that a first shot thereof in relation to the global alignment measurement, is placed below the mask membrane 102.
(2) The fine-motion stage 108 moves the wafer 106 to change the spacing (hereinafter, xe2x80x9cgapxe2x80x9d) between the mask 101 and the wafer 106, from a gap for stepwise motion to a gap for gap measurement (hereinafter, xe2x80x9cautofocus (AF) measurementxe2x80x9d). Then, the AF measurement is performed by using gap measuring means, not shown.
(3) The parallelism between the mask 101 and the wafer 106 is corrected by using the fine-motion stage 108. Subsequently, any deviation between the mask 101 and the wafer 106 with respect to directions along the surfaces of them, is measured at plural points. Then, correction amounts for positional deviations of respective shots are calculated.
(4) The rough-motion stage 109 operates to move the wafer 106 so that a first exposure shot of the wafer 106 is placed below the mask membrane 102. Then, any positional deviation of the first exposure shot with respect to directions along the surface thereof, is corrected by means of the fine-motion stage 108. Thereafter, by using the fine-motion stage 108, the gap is adjusted to set the exposure gap there.
(5) An exposure is executed.
(6) The fine-motion stage 108 operates to retract the wafer to a position for the gap for stepwise motion. Then, the rough-motion stage 109 moves the wafer stepwise, so that a second exposure shot thereof is placed.
After this, the operations (4)-(6) are repeated, by which exposures of a predetermined number of shots on the wafer are accomplished.
Generally, a mask membrane is a very thin film of about 2 microns in thickness. Also, a mask and a wafer (substrate) are placed very close to each other with a small clearance held therebetween. If, therefore, the gap adjustment is performed to change the gap between the mask and the wafer, while the mask and the wafer are held opposed to each other in an area larger than a certain area, the mask membrane may deform so as to cancel the change in volume of the gap during the gap adjustment. Further, as the mask membrane and the wafer are opposed to each other, it takes a long time until the deformation of the mask membrane is attenuated. This causes deterioration of the exposure transfer precision or of the alignment measurement precision. Particularly, when the gap adjustment is made to enlarge the gap between the mask and the wafer, the membrane will deform toward the wafer side, such that there is a possibility that the membrane contacts the wafer.
The exposure operation or the alignment measurement cannot be started until deformation of the mask membrane is attenuated. This leads to a decrease of throughput.
It is an object of the present invention to provide a semiconductor exposure apparatus by which the exposure transfer precision as well as the alignment measurement precision can be improved significantly, and also by which a driving path of a stage for a substrate, such as a wafer, can be optimized for enlargement of the throughput.
It is another object of the present invention to provide a device manufacturing method by which efficient production of microdevices can be accomplished.
In accordance with an aspect of the present invention, there is provided an exposure apparatus, comprising: gap measuring means for measuring a gap between a mask, having a mask membrane, and a substrate; gap adjusting means for adjusting the gap; and driving means for relatively moving the mask and the substrate; wherein said gap adjusting means adjusts the gap when the mask and the substrate are placed at a position whereat they are opposed to each other in an area smaller than a predetermined area.
In one preferred form of this aspect of the present invention when the area in which the mask membrane and the substrate are opposed to each other is larger than a predetermined value, the gap adjustment is performed after moving the mask and/or the substrate to a position whereat the mask and the substrate are opposed to each other in an area smaller than the predetermined value.
The position for the gap adjustment may be determined in accordance with X-Y positional information on a substrate stage, for holding the substrate, before and after the gap adjustment.
Positional information on a substrate stage, for holding the substrate, may be produced in accordance with a shot layout of the substrate and a shot whereat the membrane and the substrate are opposed to each other.
An area in which the mask membrane and the substrate are opposed to each other may be calculated on the basis of positional information about a substrate stage for holding the substrate, and a state of opposition between the mask membrane and the substrate may be discriminated in accordance with a result of the calculation.
The state of opposition between the mask membrane and the substrate may be discriminated in accordance with a shot layout of the substrate and a shot whereat the membrane and the substrate are opposed to each other.
The order of shots may be determined in accordance with a current position of a substrate stage and a target position of the substrate stage.
The adjusting means may perform gap adjustment by moving the substrate in a tilt direction.
The driving means may move the substrate in a direction parallel to the surface of the substrate.
The driving means may move the substrate stepwise.
In accordance with another aspect of the present invention, there is provided a device manufacturing method, comprising the steps of: coating a substrate with a photosensitive material; exposing the substrate by use of an exposure apparatus as described above; and developing the exposed substrate.
In accordance with a further aspect of the present invention, there is provided a gap adjusting method for adjusting a gap between a mask and a substrate disposed opposed to each other, said method comprising the steps of: relatively moving the mask and the substrate relative to each other, to a predetermined position whereat a portion of a membrane of the mask is not opposed to the substrate; adjusting, at the predetermined position, the gap between the mask and the substrate, to a desired gap; and positioning, after the gas adjustment, the mask and the substrate into a desired positional relation with each other.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.